MAINTAINERS: Add entry for APM X-Gene SoC PMU driver

This patch adds the MAINTAINERS entry for APM X-Gene SoC PMU driver.
Signed-off-by: Tai Nguyen <ttnguyen@apm.com>

MAINTAINERS

@@ -856,6 +856,13 @@ F:	drivers/net/phy/mdio-xgene.c
 F:	Documentation/devicetree/bindings/net/apm-xgene-enet.txt
 F:	Documentation/devicetree/bindings/net/apm-xgene-mdio.txt
 
+APPLIED MICRO (APM) X-GENE SOC PMU
+M:	Tai Nguyen <ttnguyen@apm.com>
+S:	Supported
+F:	drivers/perf/xgene_pmu.c
+F:	Documentation/perf/xgene-pmu.txt
+F:	Documentation/devicetree/bindings/perf/apm-xgene-pmu.txt
+
 APTINA CAMERA SENSOR PLL
 M:	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
 L:	linux-media@vger.kernel.org